Lock nuts
are very useful and are used by engineers and mechanics. The diagram below
shows a wheel pushed onto a threaded shaft. Washers are placed on either
side of the wheel and a lock nut is finally threaded in position. This is
a highly effective method of securing a wheels on shafts / axles. A
close look at the lock nut shows that it has a nylon sleeve. As the nut is
tightened, the thread on the shaft / axle cuts into the nylon, holding it
firmly in position. As the wheel rotates a normal nut will loosen
because of friction and vibration of the wheel. However, the nylon holds
the nut firmly in position.

An alternative is to use two normal
nuts. The second locks the first in position.